The present invention relates to a device for clamping rotary shaft portions.
Hand brake devices, disk brake devices and like brake devices and clutch devices are well known as devices for clamping rotary shaft portions. Also known are clamp devices wherein a tapered sleeve is used for holding a shaft portion to a fixed portion (see, for example, Examined Japanese Utility Model Publication SHO 37-2711).
Such a clamp device is included in a tilting rotary table apparatus as shown in FIG. 6.
The tilting rotary table apparatus is attached to a machine tool for use in machining workpieces. The apparatus has a circular table rotating shaft 60 and a circular table tilting shaft 61. A circular table 62 is rotatable about the shaft 60 by a table rotating drive assembly 65 comprising a servomotor 63 for the rotating shaft, a worm 64, etc. The circular table 62 is further rotatable about the tilting shaft 61 by a table tilting drive assembly 70 comprising a servomotor 67 for the tilting shaft, a worm 68, a worm gear 69, etc.
The tilting shaft 61 or the rotating shaft 60 of the tilting rotary table apparatus is held against rotation conventionally by pressing a hydraulic pressure pad 73 against a brake plate 72 provided at one end of the tilting shaft 61 or by pressing a hydraulic pressure pad 74 against the periphery of the circular table 62.
When a great cutting force acts on the tilting shaft 61 of the table apparatus, exceeding the clamping force of the clamp device, the cutting force acts directly on the portions of the worm 68 and the worm gear 69 meshing with each other and is likely to damage the toothed face of the worm.
With the conventional clamp device, therefore, an increased hydraulic pressure is applied to provide a greater clamping force. However, the increased pressure, when applied to the hydraulic pressure pad 73, will cause marked wear on the tilting shaft brake plate 72 and a fixed portion 75 to shift the tilting shaft 61 axially thereof and displace the axis of the rotating shaft 60 of the circular table 62. Further if a great force is applied to press the pad 74 against the circular table, the rotating shaft 60 is likely to be warped by the force.
On the other hand, the clamp device wherein a tapered sleeve is used, exterts a great fastening force and acts radially of the sleeve, and is accordingly less likely to cause damage to the toothed face of the worm and to displace the shaft axis. Nevertheless, the shaft portion of the tilting rotary table apparatus is frequently clamped and unclamped by remote control, so that extreme difficulties are encountered in using the tapered sleeve for the clamp device.